The present invention relates broadly to battery capacity measurement apparatus and in particular to a charge depletion meter.
In the prior art one of the more reliable methods of determining the state of charge of lead-acid battery was the hydrometer test. Sulphuric acid which is commonly used in a lead-acid battery is heavier than water. Therefore, the mixture of sulphuric acid and water which is used as the electrolyte, is heavier than pure water and its specific gravity may be measured.
When a battery is fully charged, the electrolyte has a specific gravity reading of about 1.250 to 1.290. This reading means that the given amount of the electrolyte in the battery will weigh 1.25 to 1.29 times as much as the same volume of pure water. As the battery discharges, some of the heavier sulphuric acid is broken up and unites with the battery plates to form a lead sulphate coating on the plates. The remaining electrolyte, therefore, becomes lighter and lighter as the battery discharges. For this reason, it is possible to tell how much a battery has become discharged simply by measuring the specific gravity of the electrolyte.
The instrument which is used to measure the specific gravity of the electrolyte in a battery is the hydrometer. The hydrometer consists of a glass barrel with a small float inside. A hydrometer reading is taken by squeezing the rubber bulb at the top, inserting the hard rubber nozzle into one cell of the battery, and releasing the bulb to draw some of the electrolyte up into the barrel. When the electrolyte has risen to a convenient level for accurate reading, it is prevented from rising farther by a small tube. This method of measuring the state of charge of a battery is strictly manually and time-consuming. The present invention provides a completely automatic charge monitoring and measuring apparatus.
The charge depletion meter apparatus solves the problem of knowing exactly how much charge has been drained from a battery at any one time. Consequently, it is known how much charge is left in it and battery replacement can be handled on a more economic basis. Therefore, the charge depletion meter solves the problem of keeping track of consumption when a battery is frequently turned on and off or when widely varying loads are encountered.